Two principal Immunopathogenetic features characterize the autoimmune inflammatory myopathies - polymyositis, dermatomyositis, and related diseases: lymphocytic destruction of muscle cells, and humoral autoimmunity distinguished by a striking set of disease-specific autoantibodies. Although the muscle cell destruction is mediated by lymphocytes, the autoantibodies, particularly those directed against the family of functionally related but structurally diverse aminoacyl- tRNA synthetases, seem to offer a useful window on the disease and have been the focus of much of this groups research for a number of years. In the past year, new findings from the Schimmel laboratory have rekindled our interest in the special role that the aminoacyl-tRNA synthetases might play in the pathogenesis of myositis. They have found that tyrosyl-tRNA synthetase and fragments derived from it by apoptotic-induced caspase cleavage have chemokine and cytokine activity on a monocyte-macrophage cell line. We have joined with the Oppenheim lab in NCI at Frederick and with the Rosen lab at Hopkins to explore possible similar activity in other aminoacyl-tRNA synthetases, especially the principal myositis autoantigenic target, histidyl-tRNA synthetase and fragments derived from it. These experiments have only recently begun.We continue to focus attention on the lymphocytic destruction and death of muscle cells. The tissue damage in myositis is associated with a predominantly CD-8+ lymphocytic infiltrate. Furthermore, muscle is one of the few tissues in which MHC Class I is constitutively absent, but in myositis, it is markedly up-regulated on myocytes, raising the possibility that this up-regulation plays a role in initiating and sustaining the inflammation. In the past year, we have completed and published studies on the presence of co-stimulatory molecules in myositis, including the novel observation that myocytes synthesize CTLA4, the first non-lymphoid cells shown to do so. Related studies on apoptosis in myositis and cultured muscle cells have continued. The known absence of apoptosis in myositis muscle biopsies appears related to the up-regulation of the anti-apoptotic molecule, FLIP. FLIP up-regulation has been demonstrated in muscle biopsy specimens and in cultured human muscle cells exposed to pro- inflammatory stimuli.Transgenic mice in which MHC Class I is controllablyup-regulated in skeletal muscle only by the feeding of tetracycline have been made. The females, and later the males, clearly develop a severe clinical myopathy and profound histologic changes, although little lymphocytic infiltrate. In addition, they develop autoantibodies, including some found in human myositis. Studies are underway to fully characterize this illness, particularly to determine if it can be reversed by down-regulating MHC I, a therapeutic approach being tested in patients as described in project Z01 AR 41076-09 ARB.Another myositis model is being developed in collaboration with the Rosen laboratory at Hopkins in which the role of apoptosis in causing an autoimmune myopathy is being directly tested in mice. These experiments are in an early stage at present and will be continued in the coming year.We have collaborated with the group of Eric Hoffman at Childrens Hospital to explore a potential role for AAV (adeno- associated virus, a non-pathogenic parvovirus) in protecting muscle against developing an inflammatory myopathy. These studies are being prepared for publication. - myositis, polymyositis, dermatomyositis, autoimmunity, aminoacyl-tRNA synthetases, transgenic, cytokine